Recently, medical practitioners have found it useful to use robotic devices to assist in the performance of surgical procedures. A robotic device typically includes a moveable arm that comprises one or more linkages. The arm has a free, distal end that can be placed with a very high degree of accuracy. A surgical instrument designed to be applied to the surgical site is attached to the free end of the arm. The practitioner is able to precisely position the arm so as to by extrapolation, precisely position the surgical instrument at the site on the patient at which the instrument is to perform a medical or surgical procedure. One advantage of using a robotic system to hold the instrument is that the system arm, unlike the arms and hands of a surgeon, are not subjected to muscle strain or neurological actions like twitching. Thus, in comparison to when an instrument is hand held and therefore hand positioned, using a medical robotic system it is possible to hold an instrument steady, or move the instrument along a defined path with a higher degree of accuracy.
Further some robotic surgical systems are designed to be used with surgical navigation systems. A surgical navigation system is a system that is able to generate data that provides a relatively precise indication of the surgical instrument relative to the location of the patient against which the instrument is applied. When a surgical robotic system is provided with the data indicating the position of the instrument relative to the patient, the robotic system may be able to position the instrument to ensure that it is applied to the tissue of the patient against which the instrument is supposed to be applied. This substantially eliminates the likelihood that the instrument will be applied to tissue against which the instrument should not be applied.
During the performance of a surgical procedure, a number of different surgical components are typically positioned at a surgical site. For example, during a procedure to attach an orthopedic implant to the patient, tissue cutting instruments are often used to gain access to the surgical site and remove bone and surrounding soft tissue that are to be replaced. Often, joint components such as trial implants are positioned at the surgical site to determine the appropriately sized implant components that should be permanently fitted to the patient. The positioning of the implant components is tracked. Each of these instruments, implants and other components has a set of unique physical dimensions. For the surgical navigation system to accurately generate data indicating the location of a component relative to the surgical site, the system processor must have data describing the component's dimensions.
In current practice, each joint component of an orthopedic joint system is packaged separately. Due to manufacturing variation, each of these joint components has dimensions which vary slightly from others of their type. A typical knee replacement will use three or more joint components. The collective variation of these dimensions is known as dimensional stack-up. In conventional knee replacement surgery, the dimensional stack-up is relatively small compared to other potential sources of alignment and placement error such as jig placement or cut errors. Options are available for users to change joint components in order to make up for these collective errors and get a proper fit.
In navigated robotic surgery, there is an expectation that cuts will be more accurately controlled and the hand fitting previously required should be reduced or eliminated. Unfortunately, the dimensional stack-up is still present with robotic surgery, and robotic machining tolerances alone may not be sufficient to ensure proper alignment and placement.
One method of reducing dimensional stack-up size is to reduce the individual joint component dimensional tolerances. This approach requires a change in manufacturing and inspection procedures and adds cost to the process.
Moreover, in an orthopedic joint replacement procedure, for example, the practitioner may want the instrument, a cutting tool, to move in the planned path in order to precisely shape the bone to fit the implant to the bone. This precise bone shaping facilitates the precise fitting of the joint component such as an implant to the face of the bone exposed by the cutting tool. However, implants are not perfect and have tolerances for manufacture. This may end up with an imperfect fit, which is undesirable. Therefore, there is a need in the art to provide a system and method for controlling a surgical manipulator based on implant parameters in order to precisely shape the bone and facilitate the precise fitting of an implant to a face of the bone exposed by a cutting tool.